This application is based on Japanese Patent Application No. 2006-67727 filed on Mar. 13, 2006, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.
1. Technical Field
The present invention relates to liquid-ejecting apparatuses and methods for determining whether a liquid contained in a liquid container is depleted, and particularly to a liquid-ejecting apparatus and a method for determining depletion of a liquid with respect to a threshold of the amount of liquid remaining which depends on temperature.
2. Related Art
Liquid-ejecting apparatuses designed for ejecting various liquids onto an object are known. For example, JP-A-11-78065 discloses an ink jet printer including an ink jet head for ejecting ink droplets from nozzle openings onto a medium such as recording paper and an ink cartridge for supplying the ink to the ink jet head.
Such an ink jet printer requires a stable supply of ink from the ink cartridge to the ink jet head. In intermittent ejection of the ink from the ink jet head, the amount of ink equal to that consumed for each ejection operation must be supplied from the ink cartridge to the ink jet head before the next ejection operation in synchronization with the ejection of the ink.
The ink is supplied from the ink cartridge to the ink jet head by an internal pressure difference between the ink jet head and the ink cartridge. The head pressure of the ink contained in the ink cartridge tends to push the ink into the ink jet head through a channel provided therebetween. The head pressure is maintained within such a range as not to excessively supply the ink to the ink jet head. The pressure in the ink jet head, on the other hand, decreases after ejection of the ink. The ink flows from the ink cartridge into the ink jet head if the pressure in the ink jet head falls below the pressure in the ink cartridge.
The head pressure pushing the ink from the ink cartridge into the ink jet head decreases as the ink is consumed and the amount of ink remaining in the ink cartridge decreases accordingly. The ink is no longer supplied if the decreased pressure in the ink jet head does not fall below that in the ink cartridge to a certain extent.
Some known ink jet printers prevent defective ink supply using a threshold of the amount of ink remaining at which ink supply is terminated. If the amount of ink remaining falls below the threshold, the printers determine that the ink is depleted and, for example, advise users to replace the cartridge even though the ink remains therein.
General printing inks, however, exhibit a lower viscosity at a higher temperature and a higher viscosity at a lower temperature. Ink with increased viscosity experiences higher channel resistance and thus flows through the channel less easily. A certain level of pressure in the ink cartridge is thus required to supply such viscous ink to the ink jet head in time for ejection. Conversely, ink with decreased viscosity can be supplied in time for ejection even if the pressure in the ink cartridge is decreased to a certain extent.
In the known art described above, ink depletion is determined whenever the amount of ink remaining falls below a predetermined threshold, although the remaining ink can still be supplied if it has decreased viscosity. That is, ink depletion is determined even if the amount of ink remaining is at such a level that the ink can still be supplied after a temperature rise and the resulting decrease in viscosity. This wastes the remaining ink. On the other hand, no determination of ink depletion can be made even though the amount of ink remaining is at such a level that the ink can no longer be supplied after a temperature drop and the resulting increase in viscosity.